This invention relates to the accurate reproduction of information stored on optically encoded disks (CD disks). More particularly, the invention relates to an improved damper system and method for use with compact (CD) disks and CD players to obtain high fidelity reproduction of music.
The compact disc and CD player operate by digitally sampling the information or music source, and recording the sampled signal as a series of pits and lands of variable lengths formed on a polycarbonate plastic substrate coated with an aluminum reflective coating and protected by a layer of clear lacquer. A land is the surface of the substrate between the pits. Usually this digitally sampled information is represented by the transitions between the pits and lands or vice versa, and by the absence of transitions. These transitions and absences of transitions become the ones and zeros of the digital representation of the music. A modulation coding and formatting arrangement is used for organizing this digital data for compact storage and for error reduced recapture. It has become an audio standard to record and read the disc along a spiral track at a constant linear speed by rotating the disc at variable speed.
In playback, a laser beam is directed at the disc and will experience changes in the reflective light pattern during transitions from pits to lands. These changes are decoded as ones and the absence of change is decoded as zeros, the number of which depends on the length of the pit or land.
Even though the CD disc has a very high theoretical capability for high fidelity reproduction when sufficiently high effective sampling rates are employed, the musical quality of CD players has nevertheless been found limited. To some, the resultant sound quality is described as harsh, grating, lacking in musical naturalness, piercing, boomy, as having a notable loss of sound stage and presence and a general lack of naturalness.
A wide variety of improvements has been proposed to cure these deficiencies, all of which generally are directed at some specific problem. A list of improvement features includes special sampling techniques, improved A/D converters, improvements in filters, special modulation codes, particular formatting, phase shift compensation, anti-aliasing filters, separation of laser and spindle mechanisms from signal electronics into differently housed components, improved audio cables of special construction, special turntable supports such as isolating platforms for minimizing the effects of vibration and many more. The vibration caused by audio feedback and stray light have been implicated in some tests regarding audio quality degradation. Proposed vibration cures include improved subchassis construction, special suspensions, and special CD player support tables which claim to help isolate vibration caused defects. In general, CD players have been said to possess immunity to such effects, but the proposed improvements all seem to make a subtle improvement in the sound quality. Indeed, another cause of audio quality degradation may involve an inter-modulation interaction between the vibration induced fluctuations in the drive current requirements for the tracking servos which are working to remove such fluctuations as reflected into the digital circuitry and analog electronics through common connections such as power supplies.
There is therefore a need for an improved CD disc playing system which will contribute to achieving a more natural, listenable, and satisfying CD disc reproduction, especially of musical material.